Method for roasting pencil leads



DecLZO, T938. R. zuCKERT METHOD FOR ROASTING PENCIL LEADS Filed June8,193'7 fait' rvllllllvllalnnll rfllzvlrarrnnra Dac. 20, 1938.

R. zUcKERTv METHOD FOR ROASTING PENCIL LEAS 2 Sheet's-Sheet 2 Filed June8, 1937 Patented Dec. 20, 19338 UNITED STATES PATENT OFT-Ica vakia,assignor .to the firm "Koh-i-noor tuikrna L. & C.- Bardtmuth, Ces.,Budejovice.

Czechoslovakia Application June s, 1937, serial No.v 141,061

In Germany July 17, 1936 1 Claim.

The roasting of pencil leads is carried'out usually in such a mannerthat the leads are placed into rectangular graphiteorchamotte-containers and covered with coal dust or graphite powder,

5 whereupon these containers are heated in chamberor muille-furnaces. Atunnel-furnace has also been employed herefor, throughwhich thecontainers arexpushed on small carriages or ceramic balls.

This known method possesses the inconvenience that, it is practicallyimpossible to maintain a sufficiently uniform heat acting upon theindividual leads, and further to ensure that the heat acts uniformly onthe individual lead from the one end to the other. This is due partly tothe flameor flue-gas being Iconducted around the containeraand'partly tothe difference in the heat supplied l,to the bottom plate and to thesidewalls of the containers, apartl from the additional heating of thea leadends by the end walls of the containers which are heated also. On theother hand the mechanical proprties of the finished pencil leads dependto a considerable degree on the height and duration of the temperatureacting upon them, the breaking strength and the hardness ofthe leadincreasing up to a certain temperature and burning period, but dropagain if temperature and burning period are further increased.

. To overcome this inconvenience the containers,

in which the pencil-leads are locatedare ofcyv lindrical shape andpassed the one directly behind the other through a stationary heatingtube, heated from the outer side or by means of heating bodiesaccommodated in the wall of the tube, the

diameter of this heating tubebeing only slightly larger than that of thecontainers so lthat it is` still possible to convey the containersthrough the heating tube without grazing the wall thereof, butnevertheless, larger air quantities are prevented from flowing throughbetween the heating tube and the containers. Hereby a perfectly uniformheat acts upon the whole outer surface of the containers, the result ofwhich is auniform, concentrical penetration of `heat to the leadscontained in the containers. Owing to the direct succession of thecontainers, the end faces of the same remain unheated, so that the causefor a more rapid heat absorption of the leads at the ends than at themiddle no longer exists.

An embodiment of the invention is illustrated,

by way of example, in `the vaccompanying drawings, in which- Fig. 1shows in vertical section a lead burning u furnace according to theinvention.

Fig. 2 Aa cross-section on line A--B of Fig. 1 on larger scale.'

Fig. 3 shows ln larger scale part of Fig. 1 with the packing arrangementfor the gap between heating tube and containers in'cross-section. 5

Fig. 4 is la top plan view of Fig. 3.

Fig. 5 shows a single container with lid in perspective view.

As shown in Figs. 1 and 2, the leads l to be roasted are accommodated nvertical, cylindrical 1o containers 2 which descend through a stationaryvertical heating tube 3 and therefore the leads lie parallel to the axisof the heating tube. Each container (see Fig. 5) consists of a hollowcylinder 2a, open at the upper end and closedV by a l5 plane bottom atthe lower end, and of alid 2b placed on the top end of the container.This lid 2b consists ofv a plate with a. low upwardly directedcylindrical rim, designed to carry the next higher container, andA whichhas at two opposite 20 points recesses for a transverse rod designed tosupport the column of containers each time the! lowermost container isdischarged from the heating tube, as will be hereinafter described.

The heating tube 3 composed for instance of 25 three pieces is of suchsmall internal diameter that between its inner wall' and the containersonly a comparatively narrow annular gap remains which just allows thecolumn of containers to pass through the heating tube without any 30danger of grazing, whereas the passage of air between the containers andthe inner wall of the heating tube is made very diilicult. Owing to thisarrangement the heating tube is prevented from acting like a chimney andconsiderable 35 quantities of air cannot pass through the same, andunfavorably influence the efficiency of the heating as well as theregulation of the heating eiect upon the leads.

The heating tube 3 is electrically heated by 40 means of heating coils 4in the carriers 5. The space between the carriers 5 and the outer wall 8of the furnace is filled withinsulating'-mass 1; in the hottest portionof the furnace insulating bricks S -are arranged between the carriersand 45 the insulating mass. `The furnace is subdivided into five heatzones, of which the uppermost and the lowermost are not directly heated,whereas, the'middle one is most strongly heated by closely wound'coils,the number of-coil windings in the 50 upper zone (pre-heating zone) andin the lower l zone (cooling zone), particularly vinthe upper zone,being less great. In this manner the heat condition in everycross-sectional plane of the furnace can be regulated as desired.

The column of containers rests at the lower end upon a suitablesupporting device I, which may for instance consist of the rack of acrabbar, which allows the column to slowly descend in known manner untilthe lowermost container can be removed, the next higher container andwith the same the whole column of containers having been previouslysupported by a transverse rod (see Fig. 3). The supporting device canthen ascend again, the head of the rack coming to bear during the lastportion of its stroke against the lower surface of the, now lowermostcontainer so that the carrying rod can be removed,

whereupon the column of containers can descend again by the height ofone container.

Figs. 3 and 4 show a part of Fig. 1 on larger scale and illustratedetails of a packing device. designed to further prevent thechimney-like sucking up of air in the heating tube I. Just above thecarrying rod i0, whichcooperates in the above explained manner with thesupport 9, three segment-like brushes i2 with bristles I3 radiallypressed against the outer surface of the container which is at the sameheight, are arranged in a box Ii fixed on the carrying frame of thefurnace, the descending container brushing along the bristles of thesebrushes. 'Ihe brushes prevent practically any air from passing betweenthe heating tube and the container column. The concentric position ofthe brush-segments I2 can be accurately regulated by means of set-screwsi4 or, if desired, by means of concentrically acting pressure springs.

The supporting device becoming operative during the removal of thelowermost container from the container column is shown in detail inFigs. 3 and 4. The transverse rod I rests upon transverse beams i5 fixedon the carrying frame of the furnace so that these beams can be adjustedby means of screws I6.

Details of the furnace shown may be modified without departing from Vthechief idea of the invention. The heating coils may, for instance, beplaced in the bodyof the heating tube, or the axial graduation of theheating may be attained not by the differing number of the windings peraxial length unit. but by altering the thickness of the wire of theheating coil, by special connection measures and the like. Instead ofelectrical heating, which will be preferably employed owing to the easyinstallation and regulability and the fact that their cost is not highas compared with their high heating eillciency, any other kind ofheating may be selected; only such kinds of heating are excluded inwhich flue gases flow through the space between the inner wall of theheating tube and the container column. The containers may for instancebe of prismatic instead of cylindrical shape and of any desiredmulti-cornered cross-section. Instead of one single packing arrangementfor the space between the heating tube and the containers severalarrangements, for instance two or three rows of brushes may be provided,one row above the other.

I claim:

A method for roasting pencil leads in closed cylindrical containerswhich are successively conducted through a heated vertical channel,consisting in arranging the pencil leads standing in the closedcylindrical containers parallel tothe axis thereof, piling the lledcontainers one upon the other in vertical alignment to form a column ofonly slightly smaller diameter than and filling practically the entirecross sectional area of the heated channel, and then conducting thefilled containers through the heated vertical channel.

RICHARD zcImR'r.

